Just FYI, the "sun4d" (D == Dragon, I think) uses the "XBus", the Xerox
bus, which is different from the S and M busses.  I have no idea what
is actually required to support the XBus, but Sun assigned a separate
CD-ROM boot partition for sun4d machines, so apparently they had
different boot loaders and/or kernels.  (Sun also had different
sun4c and sun4m kernels, yet both NetBSD and BSD/OS have a single
combined sun4[cm] kernel, so this is not conclusive of anything.)

Chris